Given below are an Assertion (A) and a Reason (R). Assertion (A): The net dipole moment of a polar linear isotropic dielectric substance is not zero even in the absence of an external electric field. Reason (R): In the absence of an external electric field, the permanent dipoles of a polar dielectric substance are oriented randomly. Choose the most appropriate answer.
Options

Question

Given below are an Assertion (A) and a Reason (R). Assertion (A): The net dipole moment of a polar linear isotropic dielectric substance is not zero even in the absence of an external electric field. Reason (R): In the absence of an external electric field, the permanent dipoles of a polar dielectric substance are oriented randomly. Choose the most appropriate answer.

Options

G1 Physics · Accepted Answer

A polar dielectric molecule can possess a permanent molecular dipole moment. However, in the absence of an external electric field, the dipoles are randomly oriented because of thermal motion. Therefore their vector sum over a macroscopic sample is zero, so the net dipole moment of the dielectric is zero. Thus Assertion (A) is false. Reason (R) is true. Correct option: D.